Fire alarm system



April 21, 1953 SLUBIN ETAL 2,636,164

FIRE ALARM SYSTEM Filed April 25, 1951 2 Sl-IEETS-SI-IEET 1L EXISTING TRANSMISSION LIIIE 20 REMOT I MODULATOR w Y i W I CARRIER ao CARRIER CURRENT CURRENT 20 H GENERATUR RECEIVER 50 PM W LU Z ,J

z 193 9 0'1 2 2 164 w z E I- i 0 CL I- 5; 85. 3 l a a E FIG. 4

I: POWER 3 I SUPPL E I U LU 2Z0 2 b INDICATOR CONTROL INVENTORS. 5 9 .L SAMUEL uau JDHNEATKINSDN, 2 240 AND LEON PDDOLSKY BY SIGNAL LIGHT euzzER 0mm April 21; 1953 s. LUBIN ETAL FIRE ALARM SYSTEM Filed April 23, 1951 2 SHEETS-SHEET 2 Patented Apr. 21, 1953 Samuel Luhin, Pittsfield, Mass., John F. Atkinson,

Arlington, Va, and Leon Podolsky, Pittsfie'ld, Mass, assignors to Sprague Electric Company,

North Adams, Mass.

chusetts corporation of Massa- Application April 23, 1951, Serial No. 222,422

"7 Claims. 1

The present invention relates to lire alarm systems that can be readily and inexpensively installed in smaller cities and towns.

Wired fire alarm systems have become firmly established in modern cities, but prior art sys tems of this type are relatively expensive; and are beyond the means of most towns. There is accordingly a between the age .old central fire gong or siren only suited .for volunteer .fire departments of very small communitties, and the standard telegraph type of fire alarm system in dispensable for large cities requiring several hundred individual fire alarm signal stations.

Among the objects of the present invention is a fire alarm system of the wired type which can be very readily and inexpensively installed.

Additional objects of the present invention include lire alarm systems that can he used with pie-existing transmission lines without interfaring with the normal use of these lines. A further object of the present invention is the provision of a self-monitoring lire alarm system which is reliable in operation.

The alcove as well as still further objects of the present invention will be more l-readily understood from the Iollowing description of several of its exemplifications, reference being made to the accompanying drawings wherein:

Fig. 1 is a diagrammatic representation of one form of fire alarm system according to the present invention;

Figs. 1a and 1b are simplified somewhat diagrammatic detail views of one type of the signal stations shownin Fig. 1;

Fig. 2 is a schematic view of thexessential details of another signal station suitable Ltor use in the embodiment of Fig. .1.; and

Figs. 3 and 4 are diagrammatic showings of portions of an indicator assembly suitable for use in the embofiment of Fig. 1.

According to the present invention, there is provided a fire alarm system having a central high frequency current supplystation .anda plura'lity of individual signaling stations each including a modulating .for connection to a pre-existing electrical line such as a power supply, street lighting line .or I elephone line, to modulate the high frequency currents. Eachstation has a difieren-t characteristic modulating irequency and externally operable signal control structure connected to the modulating unit for operation to signal a .fire alarm by changing the operation of the modulator unit. vAt Irh81$fim8 or a diiierent central location an indicator assembly can be connected to the line to separately indicate the presence of individual modulations and thereby indicate the signaling the source of specific fire alarm-s.

Referring to the form of the invention shown in .Fig. l, .10 indicates a -pontion of a nrewexisting street lighting line, power line or telephone line of a town or small city, the line usually branching over substantially the entire population area. Individual signaling stations are shown at 2B and can .be connected at suitably spaced individual locations along the branches of the line. Each station has a remote modulator unit represented by the legend in the figure, and an external signal control handle .22 for operation to signal an alarm. In this embodiment high .frequency currents are applied to the line It by a carrier current generator 3J6. vAt a central location an indicator assembly including a carrier current receiver 4t and an indicator unit 50 are connected to the line to {indicate the signaling of afire alarm.

The carrier current generator can he of any suitable type that impresses upon the line It! the desired high frequency currents. One highly effestive form of such construction is shown in the copending' Atkinson et a1. U. S. patent application Serial No. 75%,422, filed June 27, .1947, and the details of the generator connection there do: scribed are hereby incorporated in the present application as though fully set .forth herein.

For signaling stations '20, there can be used any type of modulating arrangement to impart one or more characteristic identifiable modulations to the carrier currents. The modulations of the individual stations are conveniently made easily distinguishable from each other by effecting these modulations at di fierent frequencies as described. in the above-mentioned copending application or in the copending Atkinson et a1. U. .S. patent application .Serial No. 171,628, filed July 1 .1950. For distinguishing alarm signals from the indications accompanying equipment failure, the alarm indicating modulations can be coded as by periodic interruptions, or can likewise he represented by differences in modu: lation frequencies.

Fig. la shows one form of coded modulator type of signaling station 253. A toothed wheel 3! is arranged to rotate around .a supporting shaft 32 as by any of the well-known fire alarm signal box constructions. Examples of these constructions are shown in U. .S. .Patent No. 2,343,964 issued to .F. C. Evans on March 14, L944, U. S. Patent No. 2,159,395} granted May .23, 1939, to J. H. Wheelock, and U. S. Patent No. 1,875,810 to G. .F. Harter .dated September 6, 193.2. In the interest of clarity the particular mechanical details tor rotating the wheel are not reproduced in Fig. la. These constructional teaturesare well known,one common form involvingessentially a spring drive that is wound by the manipulation of :an alarm signaling 22 and then drives the wheel through one or more revolutions. Grooves 36 are shown as distributed around the wheel to coact with a follower All which is held against wheel as by spring 42 so that it engages and follows the teeth and grooves. A set of contacts M is suitably arranged for operation by the follower to actuate the modulator 52, as by leads 45, 4'6. Whenever the follower drops into a groove 35, the contacts close. Accordingly as the wheel rotates, a sequence of interrupted modulation is effected.

Fig. 1b shows one Way of operating a modulator through the contacts M. The circuit of Fig 1b is taken directly from the above-identified Atkinson, Kelley and McCutchen applications with the grid lead to the amplification stage broken and the broken ends connected to contact leads 45, 46, respectively. It is preferred that the ground return circuit of this grid be on the grid side of the break so that the grid is never left floating. For a more complete description of the remainder of the modulator, reference should be made to the last-mentioned application. The power supply of Fig. 1b can be the same transmission line It to which the modulator output lead is connected, particularly where this line is an electric power supply line. Where line It) is a conventional low frequency telephone circuit, energizing power can be supplied through this line or by means of an external source local to the signaling station, or by batteries such as the longlived alkaline amalgamated zinc-mercuric oxide type of dry cell. Electric power supplied over a telephone line can conveniently be of the kind that does not interfere with telephone conversation. Direct currents are quite suitable for this purpose.

Some telephone lines, particularly those having a single separate circuit for each subscriber,

do not have an interconnected network but are instead formed of a multiplicity of separate, unconnected individual lines. With this arrangement the central fire alarm station can be conveniently connected to or located at the telephone exchange inasmuch as all the individual telephone lines are connected to this exchange. The desired carrier currents and alarm signals can then be operated through any convenient number of individual lines. To keep the lines separate, they can be coupled through filter circuits that permit passage of the high frequency carriers, but block the transfer of low frequency telephone sig-' nals. A small capacitance is all that is needed for such connection. Alternatively, a separate carrier generator can be provided for each line.

At the central station the carrier current receiver 40 and indicator to are connected to detect and indicate the alarm modulations, as by audible and/or visual means. A set of simple or conventional demodulator amplifiers similar to those shown in the aboveeldentified copending applications, and a gong actuator is all that is needed. The repeated sounding of a gong will then indicate a fire alarm, and an individual station indicator will show to which location the fire-fighting apparatus should be dispatched.

Should the receiving of modulations be interrupted by reason of equipment failure rather than the signaling of an alarm, only a single sounding of the gong will take place so that the distinction will be unmistakable. In addi tion the indicator lights will flash on and off only when an alarm is sounded.

If desired, the interrupting wheels 3| of the individual station can be distinctively coded so that the modulation interruptions and the gong sounding will be correspondingly coded to directly indicate the location of the alarm-giving station. r

cies.

To make it unnecessary for someone to be in constant attendance and accurately note such gong striking, the code wheel is arranged to go through more than one alarm-sounding cycle. The first or second cycle generally attracts sufiicient, attention so that the third or fourth cycle can be interpreted without difiiculty. A tape punching mechanism can also be operated to recordthe location'of the alarm. For this purpose a standard tape puncher can be connected so that it punches in resonse to each interruption of the modulation from any station. The interruption code will then be reproduced by the punch marks to indicate the sourcce of th alarm.

The signaling station shown in Fig. '2 is operated by modulating the carrier currents at a characteristic and identifiable frequency different at every station. For this purpose it includes an oscillator circuit we having a pair of contactless mechanically selective low frequency transfer units I93, I94 connected to an'electron discharge unit I95, for determining specific os.- cillating frequencies corresponding to the de-] sired modulating rates. Discharge unit I96 is incorporated in an evacuated electron-discharge tube I5I and includes a grounded cathode I91, a control grid I98 and an anode M9. The grid I 98 is connected to the cathode by means of grid return resistor I02, and by means of con-; denser Hi4 is connected to the movable pole H9 of a single-pole double-throw switch operated by handle 22. The two fixed contacts III and II2 of this switch are connected to the common or ground return conductor IZil through the respective outputwindings H3 of the low frequency transfer units I93, I94. A condenser I03 connects anode I99 in parallel through both' of the input windings In to ground. A peak; ing condenser I I 6 is shown as connected between the switch pole Ill! and ground toincrease the elficiency of the transfer units by helping to tune their output windings of the oscillating frequen-' The oscillator is energized by connecting anode: I99 through load resistor I3I to the positive lead Ill of a direct current supply I89, the negative terminal of which is grounded as shown. The direct current supply I89 is of conventional form and is shown as a rectifier and filter assemblyto maintain the oscillator operating under ap-;

proximately constant voltage. The oscillator I95. develops a sinusoidal voltage which is impressed, by meansof coupling condenser I35 on the input grid I42 of an amplification stage I40 in the, usual manner. From the anode I 50 of this stage, amplified oscillations are taken by way of coupling transformer I55 and applied to the anodes I58 of'a diode rectifier not. The cathodes lszj of the rectifier return to ground through an ad justable inductor I66. A capacitor I16 alsocon nects the cathodes to the desired transmission line.

As explained in copending Atkinson et a1. U. S. patent application Serial No. 171,628, filed July 1, 1950, the anodes I58 of rectifier Itt are suitably biased by connection through series resistor I68, and voltage dividing resistor I79 to the lead I'II of the direct current supply I80. As also ex goo -1n Flamed mow last-meationcd-pateni; application,

don will be sinusoidal in accowdance wiih the,

oscillator 185. This oscillation frequency .is determined by the mechanical-1y "selective characveristios of transfer units [-93, I94 which have a pan-oi matched vibrating magnetic reeds 134., 35 each magnetically linked with the respective windings l l, HSond mechanically interconnectedso that vibrations of one will b chansml bfcd to 131181321181 if they correspond very closely in frequency to iihehat-ural frequency at the other will vibrate who details of "several typeszoi such transfer units are more compleicly sctfiorih in theAtkihson of al. application Serial No. 1'11,s2'a.-

By suitabloradiustmema and selection, the individusd transfer units are arranged to respond and pass only a relatively restricted range of frequencies. the range of any nnit' being diifercnt from that of any other mail in the entire combinaoion of signaling stations. "The indicator unit 50 is connected to sharply distinguish the individual I modulation ranges, and can have identical transfer units connected for this purpose, as disclosed in the last-mentioned application.

3 shows the essential elements of an in dividual portion of one .form i indicator unit of the present invention. suitable for operation with the remote modulator of A relay .246 is connected by leadlill, fixed contact arm 254., and

movable contact arm 248 to one terminal of powerusupply unit 218 having its other terminal grounded at 22 0 The relay operating circuit is completed through an indicator control unit 24!. which is operated by signals passed by a preceding selective-circuit. A reset switch 240 having normally open contacts is shunted across between arm .254 and blade 248. An additional flxcdcontact arm 252 is cor-unveiled to energize signaling devices such as signal light 230 and buzzer 2-32 when blade 24B is in contact with arm 252 The movable blade is biased. as by she spriuginess oi the blade itself, toward engagement with. arm 252 but upon energization of relaw 245., is pulled away irom arm 25.2 and brought into contact with arm 254.

The indicator control circuit 240 is arranged as. by any convenient or well-known construction-to keep the relay 246 energized so long as the desired effective signals are not being receivcd, and armMB is maintained in the actuaced, position shown. This causes the relay to hold itsamnature 248 out of contact with arm 25-2,, andprevenls operation of the indicator. Upon receipt of the selected signals the indicator control circuit is arranged to increase in resistance so that the relay becomes deenergized, and. armature "2 springs back into contact with arm 252. This closes the energizing circuit for the indicator light and buzzer and at the same time opens the lock-out circuit between contacts 254 and 248. The indicators are accordingly kept actuated even though the reception of the selected signals is only momentary, enables accurate notation of the fire alarm indication. When the indications are no longer needed, switch 2| 0 can be operated to momentarily close the shunting.

circuit. This energizesthe. power supp y circuit to relay 206., the selected sicn-alsa'rc no longer being received. Armature 243 will accordingly be pulled over to chelposiiion shown in the .ugur

the indicator, light and buzzer willstopoperat mg and ,the apparatus will be ready for um next fire alarm.

The circuit of Fig. '3 can be arranged to sueszpond only in those modulation irequeucics which are supposed to indicate the s gnaling of a lire alarm. This oonresponds to the modulatlog frequency controlled by transfer unit 194 in the apparatus of Fig. '2. An additional indicator circuit such as those shown in Fig. 3 can be arranged to respond to the modulations controlled by transfcr unit 188, but this indicator need not have the locl -out ice/tare showdin Fig, 3 and furthermore need not have the buzzer 232, but may be of the same type shown in the aboveidentified application Serial No. 171,628.. "This last indicator will accordingly monitor the apparatus and give a warning indicationrwhenever any portion of the line, signaling stations, power supply, etc. i ails to operate properly.

Fig. 4 shows one highly efiective form of indicater control circuit 24-0 for the combination shown Fig. 3, and is constructed by merely reversing ihe signal and bias pol-armies for the corresponding indicator shown in 3 of applica tion Serial .No. 171,628. The bias will accordingly' @keep the relay control stage a l; a relatively low impedance until the negatively polarized rectified signal voltage is impressed on the input of this-stage.

In place of the grid-circuit-opening control I as shown at Figs. lb and '2 for example, 'the alarm-sounding circuit at iihe remote modula tor can be arranged to control the plate circuit,

brought mic vibration of suoiciene amplitude for proper operation.

For reducing the power consumption of iheao paratus, the electron-discharge tubes used may be of the so-called battery operated fill/De of vacuum tubes which have directly heated cath odes and provide the desired operation with a minimum of commie-heating energy. In addi tion dry .rectifiers or crystal diodes can be substituted for the two diode stages of tube I For example. Inasmuch as dry roctifiers and meal diodes operate Without requiring separate heatingcurrents, they reduce the power consumption of the apparatus.

In place of the lock-out type of indicators described above, the control handles 22 .may be arranged to automatically lock when brought into fire alarm indicating position. A special unlocking mechanism may be provided, and may even be key-controlled, to permit return movemeni: of these handles. The re'turn of iihe hanthat; answers the alarm.

If desired, the audible alarm signals may be operated by means of a set of relay contacts map This climi arate from those that operate the signal light.- Since the-audible signals need only be used to warn a Watcher to look for the signal light, a single buzzer or gong can be connected for operation'by all 'of the control relays individually. It is advantageous to have signal lights that are colored differently to indicate different operating conditions. Such an additional signal light can also be connected between contact 25d and ground in the construction of Fig. 3 to show that the relay is operating properly.

The alarm closing circuits need not be controlled by mechanically moving relay parts, but can be operated with electron-discharge tube controls. Thus, a warning light or buzzer can be substituted for the relay of Fig. 4 in the plate circuit of the electron-discharge control stage to which it is connected. The light (or buzzer) will accordingly be adjusted so that it remains lit at all times except when the selected signals are impressed on this stage. By having the light of the arc-discharge type'and arranging so that th'e circuit does not have sufficient voltage to cause an arc to strike except when a special reset switch is operated, the lightwill automatically lock itself out.

A feature of the above forms of the present invention is the fact that not only are'th'e ap-" paratuses completely self monitoring, but there can be no confusion between any number of alarm signals even though they be sounded simultaneously. In each case an alarm is limited to a characteristic modulation frequency and can operate an individiual visual indicator. Anynumber of alarms sounded at the same time will merely cause the actuation of the corresponding number of individual indicators, and simple ob servation will readily show which indicators are being actuated simultaneously. I Where installations have only a limited numberof alarm stations, there is no need for "the sharp selectivity of the more expensive contact less mechanically selective transfer units, In their place there can be used ordinary resistancecapacitance or inductance-capacitance types of oscillators such as those described in Radio Engineers Handbook by F. E. Terman, Copy right 1943 by McGraw-Hill Book Co., Inc., Section 6, pages 480-484 and 503 to 511. The resist ancecapacitance form of oscillator described'on pages 505 and 506 is particularly suitable inasmuch asit dispenses with the need for a'n'induc-- tor-"which particularly at the lower carrierfrequencies would be relatively expensive. Y

As many apparently widely different-embodimerits of this-invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof, except as defined in the appended claims. I g

What is claimed is:

1. In a fire alarm system for use with a pre-. existing line connected for transmitting low frequency electric currents for other purposes, carrier current supply elements for impressing high frequency electric currents on the line, a plurality of individual signaling stations 'each including a modulating unit, for connection to the line to modulate these high frequency currents, each, station having three different modulating characteristics, said three modulating characteristics consisting of a constant first modulation to indicate an operative system, an absence of said first modulation to indicate a 8- fault "or failure "in the system, and a second type modulation to indicate the signalling of a' fire, externally operable signal control structure connected to each station for operation to signal a fire alarm by changing the operation of the modulator unit to produce said second type moduation, and an indicator assemblyfor' con nection to the line to separately detect and inch--- cate the presence of the individual modulation characteristics and thereby indicate the signal ing and the source of specific fire alarms while simultaneously monitoring said system.

2. The combination as defined'by claim 1 in which the individual modulator units include contactle'ss mechanically selective elements connected for very accurately fixing the modulating frequency; and the indicator assembly includes a band-pass stage-connected to selectivelyreceive and passa band of high frequencies including the modulation characteristics of all the individual stations, and 'conta'ctless mechanically selectiv elements connected to sharply respond tdthje' precise individual modulating frequencies.

j 3. The combination as defined by' claim 1 in which each modulating unit includes a principal modulating "frequency constituting said first modulation and a keying devic'e"oonnected for operation to repeatedly interrupt the modulation in a characteristic manner to produce said second type modulation. I

4 The combination as defined bycla'im 3 in" which the signal control structure of; each station is connected to have a non-operated and an 0p-'i erated position, and to effect modulation at acharacteristic frequency when in the non-operated position for thereby indicating that the system is in operating condition.

5. In a self-monitoring fire alarm system, a carrier current supply unit for connection to 'im-' press a high frequency electric current on a transmission line, a plurality of individual signaling stations each including" a modulating unit for connection'tc the line to'modulate the high ire quency current, each modulating unit having two diiierent characteristic modulating rates and in cluding operable signal control structure connected for operation to signal a fire alarm by shifting the modulating rate from one to the" other, and a central indicatorfas's'embly for con-" nection to the line to separately detect and indi cate the presence of the individual modulations ior both monitoring the system and indicatingfire alarm signals. 1 5

-6. The combination 'set forth in claim 1 in which sai transmission line is an electric towersupply line; I

7. The combination set forth in claim :1 in which said transmission line consists'of a plurality of separate low frequency telephone lines and said central indicator is connected to each of said separate lines by high frequency band pass filtering units, said individual modulating units being connected to respective ones of said sepiarate lines.

. SAMUEL LUBIN. JOHN F. ATICINSON.

LEON PODOLSKY.

References Cited in the file of this patent Fischler Nov. 13, 1951- 

